In many medical environments, a medical fluid is injected into a patient during diagnosis or treatment. One example is the injection of contrast media into a patient to improve CT, Angiographic, Magnetic Resonance or Ultrasound imaging, using a powered, automatic injector. The contrast media used in these applications is typically expensive and therefore is preferably conserved to the extent possible.
During injections of this kind, it is typical for the injector operator to first mount a syringe to the injector and fill the syringe with contrast media from a separate bulk contrast media container. Then, one end of a translucent tube is coupled to the syringe, and the other end of the tube is connected to a needle or catheter and inserted into the patient, permitting subsequent injection of contrast media into the patient.
Often, during the procedure, the operator briefly withdraws blood from the patient into the catheter to check for patency of the catheter, by running the injector backward to withdraw blood from the catheter or needle and into the translucent tube. If blood is visible in the catheter after this brief withdrawal, the operator can confirm that the needle or catheter is not obstructed, for example by blood clots. Thereafter, the operator proceeds with the injection, by running the injector forward to force contrast media from the syringe into the patient.
In angiographic applications, often small injections of contrast media are made during final positioning of the catheter, in order to visualize the vasculature of the patient and position the catheter in relation to that vasculature. (Small contrast media injections are necessary because the catheter is not visible under fluoroscopy.)
One difficulty with the procedures described above is the need to decide, early in the process, the amount of contrast media to place in the syringe. For safety reasons, any contrast media remaining in the syringe after an injection cannot be reused on another patient. Therefore, due to the cost of contrast media, it is desirable to fill the syringe with only the amount of contrast media that is needed for the injection. Unfortunately, this amount is difficult to predict accurately. Overestimation of the needed amount results in wasted contrast media. Underestimation requires that the syringe be refilled; this involves disconnecting the syringe from the tube, connecting the syringe to the bulk contrast media container, withdrawing additional contrast media into the syringe, and then reconnecting the syringe to the tube. This refilling operation is not only tedious, but it also creates safety hazards due to the possible introduction of air into the catheter during disconnection and re-connection, and possible exposure of the operator and/or contamination of the bulk container by contrast media in the syringe which has potentially been exposed to the patient's blood.
Another difficulty arises during catheter positioning, when making small injections of contrast media to aid in visualizing the vasculature of the patient. To preserve sterility, the physician typically does not directly operate the power injector, but must orally communicate commands to the injector operator; this can be difficult to coordinate because the physician is simultaneously manipulating the catheter and watching the fluoroscope. Furthermore, some power injectors for injecting contrast media are designed for high flow rate injections and cannot be precisely controlled for small volume injections. As a result, when using these injectors often more contrast than necessary may be consumed during catheter positioning.